Have OpenBSD 4.6 installed on a Sun Sparc Ultra-10 with two 9 GB drives. Installed on wd0. I want to use the second drive, wd1, as a spare drive in case wd0 fails. I don't want to recompile the kernel to add RAID support, so I used dd to copy wd0 to wd1.

After dd completed the boot-device was set to disk1 and I rebooted. However, when OpenBSD came up on wd1 it mounted everything as read-only. I've used dd before on Solaris to duplicate boot drives, but 'm unsure why it didn't work this time with OpenBSD.